The present invention relates to a warming fan, and more particularly to that type of warming fan with a speed reducing device by which the revolution speed of the fan can be kept low enough and torque of the same can be kept high enough.
As is well known, the type of fan with a heating device is in fashion in todays domestic appliance market because it may be used for a warm breeze on cold days and a cool wind on hot days just by switching the heating device or or off. The conventional type of warming fan generally comprises a fan set, a power set for driving the fan set, a heating device installed on one side of the fan set and an electrical control device for controlling the power supply of the power set and the heating device. The power set of a conventional fan is always a single phase inductive motor which comprises a starting inductor and a running inductor. As is well known, when we want to get a warm breeze, we should cut down the speed of the air flow from the fan set in addition to switching on the heating device, and when we want to cut down the speed of the air flow, we should cut down the revolution speed of the fan set. The conventional fan usually has several stages for controlling the revolution speed, such as a high speed button, a mid speed button and a low speed button, but the low limit of such a conventional fan is 800 RPM, which is still too fast to allow the breeze to warm up enough. Some people try to cut down the voltage to the running inductor by a speed reducing device comprising TRIAC or SCR which is connected between the downstream of the running inductor and the power source. But this method is not practical, because, as the voltage is reduced, the torque for running the fan is also reduced positively. And, when the voltage is low enough, such as 40 volts for 300 RPM, the torque almost can not run the fan, and the fan will be burned by the heat generated by the heating device as soon as it stops.